Unit 2 skeletal system pt 2
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Questions and Answers

What is the primary function of osteoblasts in bone formation?

  • To maintain bone tissue
  • To convert fat into red marrow
  • To produce new bone matrix (correct)
  • To stimulate bone resorption
  • Which type of bone tissue is characterized by dense and hard structures?

  • Bone marrow
  • Cancellous bone
  • Fibrous bone
  • Compact bone (correct)
  • What role do osteocytes play in the bone matrix?

  • They create new osteons
  • They transport nutrients to bone marrow
  • They maintain and monitor bone tissue health (correct)
  • They are responsible for initiating bone remodeling
  • What is the significance of the periosteum in bone anatomy?

    <p>It provides a protective layer and supports vessels and nerves</p> Signup and view all the answers

    How does the body regulate calcium levels in relation to bone tissue?

    <p>Through hormonal control affecting osteoclast and osteoblast activity</p> Signup and view all the answers

    What role does parathyroid hormone (PTH) play when calcium levels are low?

    <p>Increases serum calcium levels by stimulating osteoclasts</p> Signup and view all the answers

    Which factors are likely to trigger early bone-forming cells (osteoblasts) to start developing?

    <p>Osteoclast signals and local mechanical strain</p> Signup and view all the answers

    What is the primary purpose of coupling in bone remodeling?

    <p>To achieve balance between bone absorption and formation</p> Signup and view all the answers

    What type of cells help prepare for new bone formation on the bone surface?

    <p>Reversal cells</p> Signup and view all the answers

    Which of the following is a matrix-derived factor that influences bone formation?

    <p>Insulin-like growth factors</p> Signup and view all the answers

    Which of the following bone cells is primarily responsible for breaking down bone?

    <p>Osteoclasts</p> Signup and view all the answers

    How does calcitonin function when calcium levels are high?

    <p>Inhibits osteoclast activity</p> Signup and view all the answers

    What is the main influence of osteoclast secreted factors?

    <p>Reducing bone resorption without affecting formation</p> Signup and view all the answers

    Which of the following best describes the role of osteoprogenitor cells?

    <p>They can differentiate into various cell types.</p> Signup and view all the answers

    What is the primary function of osteoblasts?

    <p>To convert osteoids to mature mineralized bones.</p> Signup and view all the answers

    During bone remodeling, which cells are primarily responsible for the reabsorption of mineralized bone?

    <p>Osteoclasts</p> Signup and view all the answers

    What type of bone tissue is characterized by an arrangement in trabeculae and irregular holes?

    <p>Spongy (cancellous) bone</p> Signup and view all the answers

    Which of the following components makes up the bone matrix?

    <p>Calcium and phosphate minerals</p> Signup and view all the answers

    Which type of bone is primarily composed of spongy bone and has a cube-like shape?

    <p>Short bones</p> Signup and view all the answers

    What is the zone of proliferation's role in the epiphyseal plate?

    <p>It is responsible for longitudinal growth.</p> Signup and view all the answers

    Which of the following cells is most abundant in mature bone?

    <p>Osteocytes</p> Signup and view all the answers

    The process by which osteoblasts and osteoclasts work together is important for which of the following?

    <p>Calcium regulation</p> Signup and view all the answers

    What structural component do compact bones primarily consist of?

    <p>Haversian systems (osteons)</p> Signup and view all the answers

    Study Notes

    Spongy Bone

    • Composed of bars and plates called trabeculae
    • Spaces between trabeculae contain red bone marrow, which produces red blood cells

    Bone Cells

    • Osteoprogenitor Cells: Non-specialized cells found in periosteum, endosteum, and central canal of compact bones. They can turn into other cell types as needed.
    • Osteoblasts: Responsible for building osteoids. They mature from mesenchymal stem cells and are regulated by parathyroid hormone and vitamin D.
    • Osteocytes: Most abundant bone cell. They connect via tunnels called canaliculi, which allow for communication and nutrient/waste transport. Osteocytes are responsible for mechanosensing and responding to strain.
    • Osteoclasts: Responsible for reabsorbing mineralized bone by pumping carbonic acid and enzymes. They are activated by osteoblast activity, which is important for calcium regulation.
    • Bone Lining Cells: Old osteocytes that no longer play a role in synthesis. They are flat and thin with little activity. When the bone lining cell peels back, it stimulates osteoclasts for resorption.

    Bone Matrix

    • Osteoid: Immature bone matrix not yet mineralized.
    • Bone Collagens: Bone is mostly type 1 collagen which gives it a rigid structure.
    • Extracellular Matrix: Mostly made of mineral (calcium and phosphate), which gives bone it’s its mechanical properties.

    Bone Types

    • Long Bones: Long shaft with two bulky ends composed predominantly of compact bone with spongy bone at the ends. They have three distinct zones:
      • Epiphysis: Region at the end of the bone, which allows for attachment at joints.
      • Metaphysis: Transitional area where most tendons attach.
      • Diaphysis: Center region that provides structural function.
    • Short Bones: Formed similarly to long bones but vary in shape and size. They are cube-shaped and primarily composed of spongy bone.
    • Flat Bones: Have a cortical shell and stiff interior. They are broad and flat, providing protection or a flat surface for attachments.
    • Irregular Bones: Primarily composed of spongy bone like the bones of the spine.

    Compact and Spongy Bone

    • Compact Bone: Dense and strong tissue that makes up the outer cortex. It’s composed of osteons (Haversian System).
    • Spongy Bone (Cancellous): Composed of trabeculae (instead of Haversian System). It is lined with endosteum and makes bone lighter, providing space for red bone marrow.

    Gross Bone Anatomy

    • Diaphysis: Medullary cavity filled with bone marrow and outer wall composed of dense hard compact bone.
    • Epiphysis: Filled with spongy bone and covered by hyaline cartilage.

    Bone Anatomy

    • Periosteum: Tough and fibrous tissue covering bone that provides attachment points for ligaments. It also contains blood vessels, lymph vessels, and nerves.
    • Bone Marrow:
      • Red Marrow: Produces blood cells
      • Yellow Marrow: High in fat and can convert to red marrow in an emergency.

    Blood and Nerve Supply

    • Arteries enter through the nutrient foramen, serving the spongy bone and medullary cavity.
    • Nerves follow similar pathways.

    Calcium Homeostasis

    • Regulated by PTH, Vitamin D, and Calcitonin.
      • Low Calcium: Parathyroid hormone (PTH) increases serum calcium levels by:
        • Increasing kidney’s ability to convert Vitamin D into its active form
        • Stimulating osteoblasts, which upregulates osteoclasts
      • High Calcium: PTH is downregulated and calcitonin is released to downregulate osteoclasts.

    Coupling and Remodeling

    • The role of coupling and remodeling is to keep bone strong and heal damage.
    • Dual Regulation: Coupling is regulated locally by mechanical strain and a variety of proteins, and systemically by Vitamin D, PTH, and calcitonin.
    • Uncoupling: When the need for serum calcium levels outweighs the need for coupling, bone absorption and formation are uncoupled to reach homeostasis.

    Coupling Signals

    • Matrix Derived Factors: The bone matrix stores growth factors including platelet-derived growth factor and insulin-like growth factors, which are deposited by osteoblasts and released by osteoclasts. These factors mainly stimulate osteoblast progenitors.
    • Osteoclast Secreted Factors: Contain anti-resorptive inhibitors that may reduce bone resorption without impacting bone formation.
    • Osteoclast Membrane Bound Factors: Osteoclasts interact directly with mature osteoblasts to promote their activity.

    Coupling Mechanisms

    • Bone breakdown (resorption) and bone formation are linked, even though they don’t happen at the same time.
    • Mechanism 1: Osteoclasts release signals that trigger early bone-forming cells (osteoblasts) to start developing. Other signals from nearby cells in the bone unit fine-tune the number and activity of bone-forming cells.
    • Mechanism 2: Other cells help pass along these signals to both developing and mature osteoblasts, including:
      • Cells that are already in the osteoblast family and are located in the protective layer over the remodeling bone.
      • Reversal cells, which are found on the bone surface and help prepare for new bone formation.
      • Osteocytes, which are mature bone cells embedded in the bone that help communicate about bone changes.

    Objectives

    • Compare and contrast osteoblasts and osteocytes.
    • Identify major long, short, flat, and irregular bones in the body.
    • Describe the process of calcium regulation in the body.

    Bird’s Eye View

    • Bones are the scaffolding of the body, performing many functions:
      • Providing shape
      • Allowing for motion
      • Protecting organs
      • Cell production in bone marrow
    • An adult has about 206 bones.

    Basic Bone Anatomy

    • Periosteum: Tough and fibrous connective tissue that covers bone.

      • Contains blood vessels for nutrient transport.
      • Contains lymph vessels and nerves.
      • Acts as an anchor point for ligaments and tendons.
    • Epiphysis: End of a long bone.

    • Diaphysis: Region between the epiphyses.

      • Medullary cavity: Hollow within the diaphysis that stores yellow marrow.
      • Yellow marrow: High in fat content and can convert to red marrow (which makes red blood cells) in an emergency.

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